An injection molding machine is generally provided with a mold clamping device for clamping a mold. In this type of mold clamping device, for example, a high-pressure mold clamping is performed at the maximum mold clamping force of the mold clamping device to achieve secure clamping without the occurrence of flash or the like; however, since an excessive mold clamping force is applied to the mold, the mold is degraded earlier and consumption energy is unnecessarily increased, and stains, such as weld marks, burns and black streaks, and damages on the surface of cavities are produced due to insufficient gas removal, with the result that it is necessary to perform repair process. Thus, if a mold can be clamped with a required minimum mold clamping force, that is, a proper mold clamping force, it is possible to avoid an excessive mold clamping force added to the mold, with the result that it is possible to extend the life of the mold, reduce the consumption energy and avoid the interruption of production and the like.
Conventionally, as the above-described method of setting a proper mold clamping force, a method of setting a mold clamping force of an injection molding machine disclosed in patent document 1 proposed by the applicant of the present invention has been already known. The method of setting a mold clamping force disclosed in patent document 1 is a method of setting a mold clamping force of an injection molding machine in which a force for clamping the mold attached to the mold clamping device is set. In this method, the mold clamping force is varied to 1/Nth (N>1) the force at a time from the maximum mold clamping force in a sequential manner; tentative molding is performed at each mold clamping force; the opening of a movable mold at a time of the tentative molding is detected from the amount of reverse rotation of a drive motor for applying pressure to the movable mold; when the opening of the movable mold is detected, the mold clamping force is varied to M times (1<M<N) the force at a time in a sequential manner; after the opening of the movable mold, a mold clamping force when the movable mold is not opened for the first time or a mold clamping force obtained by adding a predetermined extra force to such a mold clamping force is determined; and the obtained mold clamping force is set at a specified mold clamping force.